302 University of California Publications in Zoology [Vou. 13 
The depth of water at the quantitative stations ranges from 414 
to 17 fathoms (8.3 to 31.3 meters). The mean tidal range for the 
entire bay throughout the month is given by Sumner et al. as 4.52 
feet. The actual extremes during the course of the year are much 
greater, ranging from 0.4 to 7.8 at Fort Point within the Golden Gate. 
The rate of the tidal currents was determined for a number of local- 
ities to be about 1.4 knots per hour at a distance of a few feet below 
the surface. It was estimated that the mean rate of water flow over 
the entire bottom was between 0.67 and 0.75 of a knot per hour. 
The mean annual temperature for the entire bay is 12991C. The 
highest recorded temperature is 20°6C and the lowest is 620C; the 
highest of the regional means for the year was obtained in the lower 
division and the lowest in the middle division of the bay. A regional 
range of 12°65C occurs in the northern end of the bay, decreasing 
to 4°920 at Golden Gate and rising to 11°18 at the southern end. 
There is a considerable seasonal variation of temperature. During 
February the temperatures are quite uniform for the entire bay, 
being at that time lower than are those of the ocean outside the Golden 
Gate. During the latter part of April and early May the waters at 
either end of the bay are warmer than in February, whereas those of 
the middle divisions are colder than they are at the earlier period. 
At the next period the latter part of July a rise of temperature is 
noticed, the Golden Gate remaining the coolest region of the bay. 
During this period the temperature of the bay is higher than that 
of the ocean off San Francisco. In the early part of October a general 
decrease in the temperature is evident, and at this period, as well as 
in the early part of May, the ocean temperatures are nearly the same 
as those of the bay. In late November a general uniformity of tem- 
perature somewhat lower than that of the open ocean prevails through- 
out the bay. The lowest temperatures of the year occur in January, 
at which time the waters of the middle division are the warmest, while 
those of San Pablo Bay are the coldest. The waters of the bay are 
at this time and also in February colder than those of the ocean. The 
annual range of the bottom temperature for the entire bay is 8°35C. 
In the winter the bottom and surface temperatures are more nearly 
alike than in summer. 
The salinity of San Francisco Bay ranges from 3.25 to 33.27 per 
mille. The mean for the entire bay for the year was estimated by 
Sumner et al. to be 27.48. The regional annual mean is less than 16 
per mille in Carquinez Strait, while it reaches as high as 31 within 
the Golden Gate. As might be expected, the annual range is greatest 
